Numerical analysis of sweep effects in shrouded propfan rotors

Abstract

To study blade sweep effects on loss production and energy transfer a numerical analysis has been undertaken on three 10-bladed fan rotors with low-pressure ratio and different sweep. Pressure ratio and sweep are in the typical range of propfans. The results of two rotors with 30-deg forwardand backward-swept blades are compared to those of an unswept propfan rotor. The geometry of the profiles of the swept rotors on each cylindrical position is identical with that of the unswept rotor. The numerical analysis shows that the total pressure ratio of the swept rotors is lower than that of the unswept rotor over the whole span. Only in the vicinity of the hub is the pressure ratio higher in the case of the forward-swept rotor. The decrease of the total pressure ratio at midspan, by sweeping the rotor, is due to an oblique shock with lower preshock Mach number and an increase of the boundary layer at the suction side. Sweeping the rotor has the effect to induce strong radial pressure gradients at the leading edge. The deflection of the flow towards and off the end-walls due to this pressure gradient has the effect of a changed diffusion and expansion of the flow in the vicinity of the endwalls. The emphasis of this article is not to directly provide rotors with better pressure ratios and efficiencies, but to explain the basic effects by sweeping fan-rotors as references for improving the rotor-aerodynamic.